1. Field of the Invention
This invention generally relates to optical modules and methods of manufacturing the same, and more particularly, to an optical module including an edge-emitting laser diode and a light-receiving element mounted on the same substrate and a method of manufacturing the same. The light-receiving element has an incident surface, and monitors an optical output from the edge-emitting laser diode.
2. Description of the Related Art
A conventional optical module includes an edge-emitting laser diode (hereinafter simply referred to as LD) and a light-receiving element having an incident surface mounted on different carriers, because the light-receiving element receives light with the incident surface thereof so as to monitor the characteristics such as the optical outputs from the LD.
FIGS. 1A and 1B schematically show a configuration example of the conventional optical module. More particularly, FIG. 1A is a top view of the conventional optical module, and FIG. 1B is a cross-sectional view thereof. In FIGS. 1A and 1B, a reference numeral 101 is an edge-emitting LD and a reference numeral 108 is a light-receiving element having the incident surface. A backside of the LD 101 is secured to an interconnection 104a provided on a platform substrate 103. A side face of a chip carrier 102 has the light-receiving element 108 on a main surface thereof, and is secured to an interconnection 104b provided on a substrate 105. An interconnection 106a and the LD 101 are provided on the platform substrate 103, and are connected by a bonding wire 107a. An interconnection 106b and the chip carrier 102 are provided on the substrate 105, and are connected by a bonding wire 107b. The chip carrier 102 includes an interconnection, not shown, connected to the light-receiving element 108.
In the assembly process of the conventional optical module, the light-receiving element 108 is mounted on the chip carrier 102 first (a first mounting) so that a light-receiving surface of the light-receiving element 108 can receive laser light emitted from a light-emitting surface of the LD 101 effectively. Then, the chip carrier 102 and the platform substrate 103 are mounted on the substrate 105 (a second mounting). The above assembly process is complicated. In addition, there are the following problems. The conventional optical module requires two support members of the platform substrate 103 and the chip carrier 102. The optical module does not have an accurate position alignment because the light-receiving element 108 is mounted through two separate mounting processes.
There are known the following techniques of producing the module having the light-emitting element and the light-receiving element mounted on the substrate thereof. First, Japanese Patent Application Publication No. 5-175614 (hereinafter, referred to as Document 1) discloses an optical semiconductor device having a reflecting optical member such as a reflecting mirror. The optical semiconductor device disclosed in Document 1 includes the light-emitting element and the light-receiving element, the mounting surfaces of which are arranged in parallel with each other. The reflecting mirror reflects the light emitting in parallel with the mounting surfaces from a rear edge of the light-emitting element, and guides the emitted light to the light-receiving element. Document 1 proposes that the aforementioned configuration makes it possible to facilitate the production and provide a low-cost optical semiconductor device.
Additionally, Japanese Patent Application Publication No. 10-321900 (hereinafter, referred to as Document 2) discloses an optical module, in which the light-emitting element and the light-receiving element mounted on the substrate are sealed with a plastic to form a single unit, the plastic being substantially transparent to the wavelength of the light emitted from the light-emitting element. The optical module disclosed in Document 2 includes a reflecting means provided in a region of the plastic surface, the region being deviated from the light axis of the light-emitting element, to reflect the leaked lights to the light-receiving element, while the lights are being emitted from the light-emitting element. The reflecting means in the optical module having the above-mentioned configuration is provided in the region of the plastic surface, the region being deviated from the light axis of the light-emitting element, and reflects and monitors only the unnecessary leaked lights while the lights are being emitted from the light-emitting element to the light-receiving element.
Further, Japanese Patent Application Publication No. 11-238900 (hereinafter, referred to as Document 3) describes an optical module including a base body having a first element mounting portion and a second element mounting portion on a main surface thereof, a light-emitting element, and a light-receiving element. The base body has the first element mounting portion arranged adjacently to an edge of the optical fiber supporting portion and the second element mounting portion arranged adjacently to the first element mounting portion. The light-emitting element is mounted on the first element mounting portion, facing the edge of the optical fiber, and has a first edge that optically couples with the edge of the optical fiber. The light-receiving element has a surface for receiving the light, and is mounted on the second element mounting portion, facing the main surface of the light incident surface. A concave portion is provided on the base body so as to guide the light emitted from the light-emitting element to the light incident surface of the light-receiving element. The light-receiving element is mounted to partially cover the concave portion of the light incident surface. Thus configured concave portion is capable of enhancing the optical coupling efficiency, and in addition, the optical module can be downsized.
It is to be noted that the optical semiconductor device described in Document 1 has to provide the optical window portion so as to make use of the emitted light of the light-emitting element on the outside, and this increases the number of the component members. In addition, the chassis for providing the optical window portion has to be processed to have a special shape. The optical module described in Document 2 has a prior condition that the module is integrated with the transparent plastic so as to mount the light-emitting element having the light-emitting surface and the light-receiving element having the light incident surface. This limits the flexibility in the structure. The optical module described in Document 3 includes the concave portion on the platform substrate. However, if silicon, for example, is used for the platform substance, the difference in the etching rates of the surface orientations is utilized with the KOH solution as an etchant. A production process is required so that the concave portion is formed with the use of the (111) surface that has a slow etching rate. As described above, there are problems in that the production process is complicated, the extra component member is required, and accordingly, the production cost is increased in the conventional techniques.